/Engine/Source/Editor/UnrealEd/Classes/Editor/EditorEngine.h
Return the active feature level. This will be the chosen Settings->Preview Rendering Level if the Preview Mode button is highlighted or SM5 if the Preview Mode button has been clicked and isn't highlighted.
[ERHIFeatureLevel::Type](API\Runtime\RHI\ERHIFeatureLevel__Type) GetActiveFeatureLevelPreviewType() const